Exactly.... but there are a few who are making a six figure salary in microstock alone, but they work across multiple microstock companies.

You won't make a 6 figure salary from selling stock images, but that's a given right. IF you do the math you should not quit your day job.

It seems that quite a few factors would influence this - subject matter, portfolio quality, being exclusive, portfolio size, acceptance ratio, keywording, assignments, upload rate/consistency etc. I think there is quite a range in downloads per 100 images.

For me, your rule is true.
Keep working!

I love your travel pics. Keep up the great work.